1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and particularly relates to a condensing portion thereof and a production method therefor.
2. Description of the Related Art
Pixels in a photoelectric conversion apparatus to be used in a digital camera and a camcorder have been fined down, as the photoelectric conversion apparatus is miniaturized and has the more number of the pixels arranged therein. Along with the tendency, an area of its light receiving portion decreases, and consequently lowers its sensitivity, because of decreasing the quantity of a light incident on the light receiving portion as well.
In order to improve the lowering state of the sensitivity, an on-chip micro lens is formed above a light receiving portion of a photoelectric conversion apparatus to condense the light onto a light receiving portion and to inhibit the sensitivity from lowering. Furthermore, in recent years, a structure has been known which has an optical waveguide that makes use of the reflection of the light formed between the on-chip micro lens and a photoelectric conversion element.
A method for producing an optical waveguide in such a photoelectric conversion apparatus generally includes the steps of: forming a well-shaped structure in an insulation layer; and filling the well-shaped structure with a certain substance. The well-shaped structure is filled with a material having a refractive index higher than that of the insulation layer to form a high refractive index region. Then, the optical waveguide is formed in which incident light is reflected on an interface between the insulation layer and the high refractive index region due to a difference between their refractive indices and is condensed into the photoelectric conversion element.
However, as pixels are fined down, an aspect ratio of a well-shaped structure increases, which occasionally leads to the formation of a void in a well in a filling step.
A technology as shown in FIG. 5 is described in Japanese Patent Application Laid-Open No. 2003-224249, as a means for solving the problem in a filling step.
In a photoelectric conversion apparatus shown in the FIG. 5, reference numeral 11 denotes a silicon substrate and reference numeral 15 denotes a photodiode arranged on the substrate 11. Furthermore, reference numeral 12 denotes a field-insulating film arranged between adjacent photodiodes 15. There arranged above them are an interlayer insulation film 21 and a SiN film 16 having a function of an etching-stop layer for stopping etching in the step of forming an opening part of interlayer insulation film 21. An optical waveguide 22 filled with a transparent film is further arranged in the opening part of the interlayer insulation film 21. In addition, a gate electrode 17, electroconductive plugs 18A and 18B and wires 19A and 19B are respectively arranged.
In a photoelectric conversion apparatus shown in the FIG. 5, a transparent film is filled in opening parts with different sizes w1 and w2, which have been formed in an interlayer insulation film 21. The opening part are formed so that the size of the opening part in the interlayer insulation film 21 increases as the position photodiode is separated from, which can improve the filling easiness.
In addition, there is a micro-condensing plate shown in FIG. 6D described in Japanese Patent Application Laid-Open No. H06-118208. The production method is shown in FIGS. 6A, 6B, 6C and 6D. In FIGS. 6A, 6B, 6C and 6D, reference numeral 801 denotes a photoreceiving element, reference numeral 802 denotes a photoresist and reference numeral 803 denotes a high refractive index region, which is higher than the refractive index region of the photo resist 802. The method for producing the condensing plate includes the steps of: applying polymethyl methacrylate of the photoresist 802 on the photoreceiving element 801; patterning it; heating the patterned photoresist to deform it into such a shape as is shown in FIG. 6C; applying polyethylene terephthalate of the high refractive index region 803; planarizing it to form the micro-condensing plate.
However, in FIG. 5, there may be such a light as is shown by an incident light 115 that can not enter into a lower part of an optical waveguide of which the opening width is prescribed as w2 in an interlayer insulation film 21, in a plurality of optical waveguides 22, which may cause the lowering of sensitivity. The light which has not been incident on the photodiode 15 passes through an interface between an insulation film 21 and the optical waveguide 22, is incident on a wire 19 and/or a plug part 18; and reflects on them to possibly cause color mixture and noise. In addition, the light which has not been incident on the optical waveguide 22 but incident on the upper part of the wire 19B reflects on the wire 19B and/or the insulation film 21 to possibly cause the color mixture and the noise.
Furthermore, when pixels in photoelectric conversion apparatus of FIG. 5 are more fined down, it is conceivable that a difference between opening widths w1 and w2 will increase according to the arrangement of a wiring layer 19, which further decreases an amount of incident light.
On the hand, a micro-condensing plate shown in FIGS. 6A, 6B, 6C and 6D is produced by heat-treating a photoresist as described above. When pixels are further fined down, an aspect ratio in a photoresist pattern as shown in FIG. 6B needs to be further increased, and then such a photoresist pattern is difficult to be formed. Furthermore, Japanese Patent Application Laid-Open No. H06-118208 discloses a method for producing the micro-condensing plate by using a metal plating technique or a die, as another production method, but the process is complicated. In addition, when the method is applied to a photoelectric conversion apparatus, there is a concern that a defect formed by metal contamination increases noise. Furthermore, the patent does not describe wiring for reading signals out from a photoelectric conversion element or the like. Accordingly, there has been a room to further study configuration relationship among a wiring layer, a low refractive index region and a high refractive index region.